In the relevant technical field, it is known to provide for the measurement of some parameters correlated to the cooking processes in order to control said processes within the cooking chamber of an oven. Among these parameters are the temperature of the chamber, the pressure, and the concentration of water vapor, which are normally significant for the desired cooking process. For the measurement of the concentration of water vapor it is known to use sensors inserted into the cooking chamber and which utilize the correlation between said parameter and other measurable parameters. For example, sensors are known which utilize the pressure differential measurable between the input and the output of the blading of the fan disposed inside the cooking chamber. Since the pressure differential is correlated to the density of the air which varies from dry air to 100% water vapor, it is possible to measure the percentage of vapor present. Another example is provided by devices for measuring the oxygen present in the mass of air inside the oven, by means of probes suitably calibrated for such measurements.
A principal limitation in the use of sensor means for sensing the vapor concentration inside the cooking chamber lies in the temperature conditions obtainable in the cooking processes which may compromise the functioning thereof or even prevent their use. These sensors are arranged to function in environments with maximum temperatures well below the maximum temperatures which can be reached within the chamber. In addition, the presence of cooking fats inside the chamber renders measurement by means of such sensors difficult and not very reliable.
Another method for controlling the concentration of water vapor within the cooking chamber is known from U.S. Pat. No. 6,662,628. The method described therein provides for correlating the slipping of an asynchronous motor, which drives in rotation ventilation means for the air inside the cooking chamber, to the concentration of water vapor. The variation of the resistant load on the motor due to the density of the air which varies according to the concentration of vapor contained therein and to the temperature, effects a variation in the speed of the motor which can be correlated to the slipping understood as the difference between the speed of synchronism of the asynchronous motor and the speed assumed by the motor as a result of the resistant load.
This variation is in general dependent on the characteristics of the motor, the fan, the voltage and frequency of the power supply, the temperature and also the concentration of water vapor, and in the majority of cases is either too great or too small with respect to the speed which is ideal and desirable for cooking, all this rendering the application of the method not very reliable and precise from the point of view of controlling the vapor concentration in order to achieve a better cooking quality.